Researchers have identified seven factors that predict which patients initially diagnosed with depression will later meet the diagnostic criteria for bipolar disorder.

Having at least four previous depressive episodes, suicidal acts, cyclothymic temperament, family history of bipolar disorder, substance abuse, younger age at onset and male gender all significantly and independently differentiated bipolar from unipolar disorders in the study of 2146 patients who initially presented with a first episode of major depression.

After an average of 13 years, 642 (29.9%) patients were diagnosed with bipolar disorder and 1504 (70.1%) were diagnosed with major depressive disorder.

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Four of the factors identified by Leonardo Tondo (McLean Hospital, Belmont, Massachusetts, USA) and colleagues can usually be assessed at the initial depressive episode (cyclothymic temperament, family history of bipolar disorder, age at onset and male gender) and may therefore be “of particular importance for prognosis and treatment”, say the researchers.

Indeed, logistic regression modelling based on these four factors gave a highly significant likelihood ratio of 87.6 for a later diagnosis of bipolar disorder.

Further statistical analyses showed that differentiation of future diagnoses of bipolar from unipolar disorder was maximal when between two and four risk factors were present per person.

By Bayesian analysis, optimal sensitivity (70.8%) and specificity (62.2%) occurred when two risk factors were present, with 66.8% of individuals correctly classified by diagnostic type.

Discussing their findings in the Journal of Affective Disorders, Tondo and co-authors suggest that “the presence of multiple predictive factors associated selectively with bipolar disorder should raise suspicion about the risk of emergence of spontaneous or drug-associated mania, even with a current diagnosis of unipolar major depression.”

They conclude: “It is important to ascertain diagnoses and formulate prognoses early so as to guide planning for optimal clinical care of mood-disorder patients, including timely consideration of mood-stabilizing medicines and cautious use of antidepressants so as to limit risk of unanticipated and potentially dangerous mood-switching.”

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